Phytoremediation of lead in sunflower (Helianthus annuus L.) by growth-promoting rhizobacterium and neem cake

Abstract Lead causes toxicity and affects plant growth by disturbing photosynthesis and the functions of enzymes. Its removal from the soil is a challenging issue. The present investigation aims to evaluate the effectiveness of organic amendment in soil with neem cake and a plant growth-promoting rhizobacterium (PGPR), Pseudomonas aeruginosa, to reduce the effects of lead toxicity in sunflower when cultivated with and without neem cake amended soil. The experiment was performed in earthen pots (10 cm diam) containing 1 kg sandy loam soil, five sunflower seeds per pot, induced with 0.2 mM and 0.5 mM lead at 100 mL. After 30 days, the combination of organic amendment with PGPR improved the growth and the physiological performance of sunflower plants subjected to lead stress. The reduction % of lead was reported as 99% by P. aeruginosa at a specific concentration of 200 ppm on an Atomic Absorption Spectrophotometer. The plants treated with PGPR in amended soil showed healthier roots and shoots and improved carbohydrates. The PGPR-treated plants demonstrated better scavenging of free radicals, with improved H2O2 scavenging activity and peroxidase (POD) activity. Neem cake and P. aeruginosa individually and in combination significantly enhanced sugar contents and POD activity while lowering stress-induced elevated levels of phenols and ascorbic acid. The combination of neem cake and P. aeruginosa could be a promising solution for growing sunflower plants in lead-contaminated soil.